1. Field of the Invention
This invention relates to an index signal output device that is used in a floppy disk drive or similar device.
2. Description of Related Art
A floppy disk drive (hereinafter referred to as an FDD) is mainly used as a device to drive a recording medium for a personal computer. It incorporates an index signal output device to detect the rotational position of the medium to initialize the recording medium or correct its writing or reading position. This index signal output device operates as follows: a magnet attached to the rotor yoke of the spindle motor as the component of the FDD generates a magnetic flux, which is detected by a magnetic flux detector located near, the rotor yoke such as a Hall IC to generate an index signal during spindle motor rotation.
If output of this index signal is not made at a correct time, data on the recording medium cannot be correctly reproduced and, in some cases, may be destroyed. For this reason, in the FDD, a mechanical or electrical adjustment (index adjustment) is made so that the phase difference between an index signal obtained as a result of detection by the magnetic flux detector, and an index signal previously recorded in the recording medium as a positional reference signal, is within a prescribed range. In this case, the mechanical adjustment takes place as follows: the detector detects a magnetic flux generated from the magnet attached to the rotor yoke of the spindle motor, and the detector, which issues an index signal according to this detection signal, is moved using a screwdriver or similar tool and then fixed with screws, etc. The electrical adjustment is performed, for example, by delaying an index signal sent from a magnetic flux detector such as a Hall element to a mono-multi circuit by a time constant which depends on the variable resistor and capacitor connected to the mono-multi circuit. Another proposed mechanical adjustment method is that a partially protruding metal member which guides a magnetic flux from the rotor magnet is continuously provided on the coil located opposite to the rotor yoke magnet and this metal member is moved horizontally around the outer circumference of the rotor yoke.
However, all these mechanical or electrical index signal adjustment methods have the practical problem that the index adjustment work is very troublesome or a complicated structure or circuit is required, leading to a high cost.
This invention has been made in view of the above circumstances and provides an index signal output device which performs an index adjustment in a simple manner at low cost only by using the flexibility of the lead terminals of the magnetic flux detector, as well as an FDD which incorporates the same.
According to one aspect of this invention, an index signal output device has a magnet attached to a rotor yoke of a spindle motor, and a magnetic flux detector, located on the stator side opposite to the rotor yoke, which detects a magnetic flux generated by the magnet and issues an index signal, where the magnetic flux detector is movable or adjustable so that the phase difference between an index signal detected by the magnetic flux detector and an index reference signal previously recorded on a floppy disk is within a prescribed range. Here, the lead terminals of the magnetic flux detector are connected to detection signal output terminals on a printed circuit board, and the magnetic flux detector can be moved for adjustment in the direction of a relevant tangent to the outer circumference of the rotor yoke by flexing the lead terminals.
This makes it possible that, when the lead terminals of the magnetic flux detector are forced to be flexed and moved using a tool, in the direction of the relevant tangent to the outer circumference of the rotor yoke, the position for generating an index signal from the magnetic flux detector during the rotation of the magnet attached to the rotor yoke can be freely adjusted, thereby allowing this adjustment to be made easily at low cost without the need for a complicated structure or circuit.
According to another aspect of this invention, the index signal output device has a carrier printed wiring board (PWB) for supporting the lead terminals of the magnetic flux detector around the ends of the detector, where the carrier PWB can be moved in the abovementioned tangent direction with respect to a printed circuit board by taking full advantage of the flexibility of the lead terminals.
This makes it possible that the carrier PWB is moved by a given distance to a given position in the abovementioned tangent direction without causing the lead terminals to break at the ends of the magnetic flux detector and without extremely bending part of the lead terminals.
According to another aspect of this invention, the printed circuit board in the index signal output device has a slit which guides the carrier PWB inserted therein in the abovementioned tangent direction.
This makes it possible that the magnetic flux detector, held by the carrier PWB, is moved correctly in the abovementioned tangent direction, and an index signal is issued accurately depending on the amount of movement.
According to another aspect of this invention, in the index signal output device, the lead terminals of the magnetic flux detector are passed through-holes in the carrier PWB and thus supported.
This makes it possible that the lead terminals are supported stably around the ends of the magnetic flux detector with ease and reliability.
According to another aspect of this invention, in the index signal output device, the lead terminals of the magnetic flux detector are soldered to the conductor lands formed around the openings of the through-holes in the carrier PWB.
This makes it possible that even when the carrier PWB is moved for adjustment, the lead terminals are not squeezed at their connections (joints) with the magnetic flux detector and thus the connections are strong enough and reliable.
According to another aspect of this invention, the printed circuit board in the index signal output device has a slit which guides the carrier PWB inserted therein in the abovementioned tangent direction, and the carrier PWB, at its area above the top surface of the printed circuit board, has through-holes perpendicular to the slit through which the lead terminals are passed.
This prevents the carrier PWB from falling off the slit and enables it to move smoothly in the abovementioned tangent direction along the printed circuit board.
According to another aspect of this invention, the index signal output device uses an inductor as a magnetic flux detector.
This makes it possible that even when the magnetic flux detector is moved away from the outer circumference of the rotor yoke by some distance for adjusting the position of the carrier PWB, it can detect magnetic fluxes with a higher sensitivity than another type of detector such as a Hall element.
According to another aspect of this invention, the FDD has an index signal output device which can freely adjust the index signal issuing position at low cost with ease, eliminating the need for using a complicated structure or circuit.